The invention refers to phosphate glass ceramic for biological applications.
The phosphate glass ceramic according to the invention can be utilized especially as biomaterial in medicine and biology, where it makes possible utilization as biomaterial in medical applications for hard tissue or bone replacement.
Because of the development of glass ceramics containing apatite, the utilization of bioactive implant materials for bone replacement has become possible in human medicine. Because the main component of human tissue is apatite, Ca.sub.10 (PO.sub.4).sub.6 (OH,F).sub.2, there results a direct intergrowth between bone tissues and the bioactive implant. Such bioactive glass ceramics containing apatite or CaO-- and P.sub.2 O.sub.5 based on a primary silicate glass are described in DE-OS No. 2,818,630, DE-AS No. 2,326,100 and DE-OS No. 3,306,683, as well as by Kokubo et al. (Yogyo-Kyokai-Shi No. 89,1981,45).
Although a large part of the known glass ceramics have proven in practical applications to be good to excellent, it has not yet been determined what effect long-term exposure to silicon compounds has on the human body.
A series of developments have addressed this problem; glasses high in P.sub.2 O.sub.5 and CaO content, glass ceramics high in P.sub.2 O.sub.5 and CaO content, and sintered ceramics high in P.sub.2 O.sub.5 and CaO have been produced.
Glasses for the purpose of biological applications in the system P.sub.2 O.sub.5 --CaO--Na.sub.2 O-- (MgO, Bao, B.sub.2 O.sub.3) have been described by Courpied et al. (Inter. Orthopaedics 6,1982,1). The materials, however, are resorbable, do not possess any apatite crystals, and are not stable in the long term in biological media. Glasses in the system CaO--P.sub.2 O.sub.5 --Al.sub.2 O.sub.3 are described by Wihsmann et al. (Wissenschaftliche Zeitschrift der Friedrich-Schiller-Universitaet Jena, Math.-Naturwissenschaftl. Reihe 32,2/3,1983,553). These glasses are labled as biocompatible, they contain no apatite crystals and consist of ring and chain-shaped phosphate structures of a high degree of condensation. In bone, however, there are small phosphate structural elements in the form of apatite crystals.
Although sintered ceramics rich in phosphate, as described in the U.S. Pat. No. 4,195,366, U.S. Pat. No. 4,097,935 and U.S. Pat. No. 4,149,893, possess a high crystal portion of apatite or whitlockite, they have the disadvantage that the ion exchange reactions promoting bone growth are not controllable due to the alkali contents, which are too low or are missing, as well as the minimal glass phase. Furthermore, the amorphous phase between the crystals partially is considerably washed out by reactions with bodily fluids. The same applies to the whitlockite crystals, Ca.sub.3 (PO.sub.4).sub.2. Conventionally known SiO.sub.2 -free phosphate glass ceramics for biological applications, especially for bone replacements, do not containe apatite crystals. In the JP-AS No. 55-11625, the phosphate glass ceramic contains the crystal phase .beta.-Ca(PO.sub.3).sub.2. The glass ceramic according to the Zhu et al. (J. Non-Cryst. sol. 52,1982,503-510), which was produced in a sintering process from a glass and a crystalline compound, contains as main crystal phase Ca.sub.2 P.sub.2 O.sub.7, and the foam glass ceramic according to Pernot et al. (J. Mat Sci. 14,1979,1694) contains the main crystal phase Ca(PO.sub.3).sub.2.
According to the present state of art, therefore, an optimal union between glass ceramic and bone cannot be achieved.